1. Field of the Invention
The present invention generally relates to an armature core, an armature, an electronic motor having the armature, and a recording disk driving device using the motor. The present invention also relates to a method of manufacturing the armature used for the electronic motor.
2. Description of the Related Art
A recording disk drive such as a hard disk drive (HDD) is conventionally provided with a spindle motor for rotationally driving a recording disk. Such a spindle motor will be referred simply to as a “motor” hereinafter.
Recently, the HDD has been installed in portable devices such as a mobile music player, and the demand for an HDD having a small dimension is increasing.
The motor used for the HDD includes an armature core formed by laminating core plates. A core plate includes a plurality of teeth arranged to radially face a rotor magnet. Each of the teeth includes a wire-wound portion, around which a wire is wound, a tip portion facing toward the rotor magnet, and a connecting portion arranged between and magnetically connecting the wire-wound portion and the tip portion. The core plate is formed by pressing an electromagnetic steel plate, and during the pressing, the connecting portion is bent such that the wire-wound portion and the tip portion are arranged at axially different levels in an axial direction of the core plate. During the pressing, however, the thickness of the core plate at the connecting portion gets thinner and, thus, magnetic-flux saturates and core-loss increases at the connecting portion. Therefore, the rotation efficiency of the motor is degenerated.